This invention pertains to an improved method for processing a photographic element using peroxide-containing processing solutions, and more specifically to the use of improved blocked photographically useful compounds in the photographic elements which are so processed.
Recent developments in blocking and timing group chemistry have led to improvements in blocked photographically useful compounds as disclosed in U.S. Pat. No. 5,019,492. As described therein, photographically useful compounds comprise a photographically useful group, and a blocking group. The blocking group comprises two electrophilic groups, the less electrophilic of which is bonded directly or through a releasable timing group to the photographically useful group, which electrophilic groups are separated from each other by a substituted atom that enables a nucleophilic displacement reaction to occur with release of the photographically useful group upon processing in the presence of a dinucleophile, such as hydroxylamine or a peroxide.
Preferred blocked photographically useful compounds according to U.S. Pat. No. 5,019,492 are represented by the formula: EQU [E.sub.1 --(--Y.sup.1 --).sub.w --E.sub.2 --(T.sub.1).sub.x --(T.sub.2).sub.y ].sub.n --PUG
wherein E.sub.1 and E.sub.2 are independently electrophilic groups, E.sub.1 being more electrophilic than E.sub.2 ; T.sub.1 and T.sub.2 are individually releasable timing groups; Y.sup.1 is an unsubstituted or substituted atom, preferably a carbon or nitrogen atom, that provides a distance between E.sub.1 and E.sub.2 that enables a nucleophilic displacement reaction to occur with release of the PUG upon processing the photographic element containing the blocked photographically useful compound in the presence of a dinucleophile; PUG is a photographically useful group capable of being released upon processing the photographically useful compound; w, x and y are independently 0 or 1; and n is 1 or 2. These blocked photographically useful compounds are highly effective and very stable in photographic elements prior to processing with dinucleophiles.
.beta.-Ketoester blocking groups have proven to be especially advantageous, particularly when the processing solution contains hydroxylamine. However, these blocking groups can be somewhat difficult and costly to prepare.
Environmental considerations as well as materials cost reduction have favored the use of hydrogen peroxide in the processing solution. Photographic elements with much lower levels of coated silver can be achieved if an amplifying bath containing aqueous alkaline hydrogen peroxide is used in the development process (the so-called "RX" process). The image intensification or amplification method is described, for example, in Japanese Laid-Open Application No. 61/77,851 and U.S. Pat. Nos. 4,526,860, 4,469,780, 4,371,609 and 4,045,225.
According to this method, a smaller amount of silver halide than usual is incorporated in the photographic material. This type of photographic material is referred to herein as a "low silver laydown" photographic material. The low silver laydown material is exposed and the silver halide is reduced imagewise to silver metal by a developing agent. An amplifying agent then is brought into contact with a developing agent in the presence of the resulting silver nuclei which act as a catalyst for the oxidation of the developing agent by the amplifying agent. The oxidized developing agent then reacts with couplers to form dye images.
Among known intensifying agents are peroxides, halogenous acids, iodoso compounds and cobalt (III) complexes, of which hydrogen peroxide is said to have higher amplification activity. For example, at page 406 of History of Color Photography by J. S. Friedman, there is described a process of oxidizing a p-phenylenediamine color developing agent with hydrogen peroxide in the presence of a silver catalyst.
The consumption of bleaching and fixing chemicals needed to remove silver/silver halide from the film is greatly reduced in low silver films. This results in decreased environmental impact as well as materials cost savings.
A need has therefore existed for highly stable blocked photographically useful compounds which are simply and economically prepared, and for photographic elements incorporating such compounds which can be developed so as to alleviate the problems identified above. In particular, it would be desirable to provide photographic elements incorporating blocked photographically useful compounds which can be processed using processing solutions containing peroxides, in order to reduce silver costs and the environmental impact of the development process.